The present invention relates to a pipe bending machine. More particularly, it relates to such a pipe bending machine which has a bending table turnable about an axis, a bending template, and a clamping jaw displaceable relative to the bending template with displaceable carriage which carries a rotatable clamping sleeve. In such a machine both a bending template and the clamping jaw have straight and curved portions and mutually associated clamping bodies which are provided with clamping surfaces for clamping a pipe to be bent and which are spaced from one another and at the same time can be brought to an operative position.
The German document DE-AS No. 1,297,064 published in 1969 describes a fully automatic pipe bending machine for bending pipes which have interconnected arcs located in different planes. In this machine a bending template which is separable at the end of bending from its rotary drive, and an associated pipe clamping jaw are provided with a pipe groove which lies in the bending plane and are also provided with a laterally branching groove which corresponds to the course of the curved pipe. The machine also has a pressing device acting outwardly and engaging transversely the non-bent pipe directly in front of the bending template. Finally, the machine also has a return rotary device for the template separated from the drive, and an adjusting device for the bending template which is activated during pressing of the pipe by the template.
Since the bending template and the clamping jaw are formed of one-piece with the pipe groove lying in the bending plane and with the pipe groove extending therefrom, the above mentioned branching does not provide an embracing full-surface clamping of the pipe. A knot point of the straight and the branching path or groove is not possible in practice, as long as after first bending the pipe is turned for the subsequent bending pipe approximately 90.degree. in the bending plane. When it is turned by deviating values or smaller bending angle, the clamping surfaces of the grooves are so small that a bending is not practically possible, since a notcontrollable slippage takes place which prevents an accurate bending. The very small clamping surfaces lead in many cases to a damage to the pipe, such as a pressing-in in connection with a cross section reduction and grooving during a slippage.
The above described arrangement operates in the following manner: After the formation of the first curve, the bending template is fixed in its position which corresponds to the respective curve shape. After this, the loose clamping jaw is brought back to its original position. Then the bent end of the pipe is pressed outwardly under force radially to the template out of the pipe groove and turned over simultaneously into the new bending plane. When then the adjusting device releases the template, it is returned by the return turning device to its initial position. When then the pressing device for the pipe is turned off, the pipe turns either itself or under the action of the clamping jaw until it again abuts against the template so that the produced pipe curves are inserted in the branching groove of the template and the loose clamping jaw. The pipe is clamped for the production of the next curve, which is performed in a conventional manner by joint rotation of the template and the loose clamping jaw.
Since the arrangement in accordance with the above discussed German document DE-AS No. 1,297,064 does not give satisfactory results, several proposals have been developed for providing different clamping surfaces during bending of pipes. One of such proposals is disclosed in the German patent No. 2,626,202 of the inventor, in which the clamping surfaces are separated spatially from one another and are rotatable relative to the bending table.
The German document DE-AS No. 2,711,340 discloses an arrangement for cold bending of strand material, such as pipes, rods and profiles, which has a bending shaping piece rotatable about an axis and provided with a peripheral groove for receiving a strand material, and a clamping device which core rotates with the bending shaping piece and has a clamping jaw arranged on the bending shaping piece and a counterclamping jaw. The clamping jaw and the counterclamping jaw are provided with a groove which together form a receiving passage for the strand material. Moreover, the bending shaping piece has in some cases further peripheral grooves, the clamping jaws and the counterclamping jaws are provided with further different grooves associated with the peripheral groove of the bending shaping piece, and the clamping jaw with the counter jaw on the one hand and the bending shaping piece on the other hand are adjustable relative to one another for exchanging the receiving passage in direction of the axis of the bending shaping piece.
The German document DE-OS No. 3,407,499 of the Applicant discloses a machine in which the bending template and/or clamping jaw have an abutment surface, particularly a receptacle for exchangeable receipt of a body provided with the clamping surface. This body is arranged in a guide and provided with a drive which drives the body in a vertical movement into the receptacle and out of the same. In this receptacle, at the location of the body provided with a clamping surface, another body is movable in and out and provided with a clamping surface of another shape.
The above discussed three documents disclose the arrangements in which the respective portion of the pipe to be clamped must be engaged or surrounded for clamping over a complete surface, or in other words over its entire periphery. In the event of different spatial shapes which have the portion of the pipe to be clamped, for example when the pipe has an expanded and not expanded end to be clamped or depending on the preceding bending of a pipe portion, this requires completely different clamping bodies with a respective clamping surface associated with each clamping body. The prior art proposes different solutions for provided this clamping body with individually associated clamping surfaces. The above mentioned German patent No. 2,626,202 discloses the clamping bodies which are arranged on the bending template and distributed over its periphery, while they are arranged on the clamping jaw in a rotatable manner and thereby are concentrated locally. In the German document DE-AS No. 2,711,340 the clamping bodies arranged on the clamping jaw and the clamping bodies cooperating with the bending template form a structural unit which is mounted on the clamping jaw support and moved together with it.